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The aim of this study is to investigate the relationship between the structure and function of an osteocalcin derived peptide on hydroxyapatite nanocrystal formation. For this purpose, , a natural motif sequence consisting of 13 amino acids present in the first helix of osteocalcin was selected based on its calcium binding ability and synthesized in both acidic and amidic forms using solid phase method. Circular dichroism (CD) and electron microscopy were performed to examine the structure and function of synthesized peptides. Moreover, the effect of these peptides on the viability of osteoblast cells was evaluated. Electron microscopy analysis showed the formation of plate-like HA nanocrystals in the presence of amidic peptide. In contrast, amorphous calcium phosphate was formed in the presence of acidic peptide. CD spectra analysis confirmed the random coil structure with lower molar elipticity for amidic peptide. In addition, the amidic peptide significantly increased the proliferation of osteoblast cells. It is concluded that increased bioactivity, which only occurred in amidic peptide is attributable to C-terminal amidation. It is also proposed that peptides with the ability to promote HA formation have the potential to be utilized in hard tissue regeneration high bioactivity and biocompatibility.

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Microbial calcium carbonate, by bridging sand particles, can play an important role in sand dune stability. A study was carried out on the cementation of sand grains and infilling of pore spaces by CaCO₃. Two bacterial species (Sporosarcina pasteurii and Sporosarcina ureae), three reactant concentrations (0.5, 1 and 1.5M), and six reaction times (12, 24, 48, 96, 192 and 288 hours) were tested in factorial experiment. Bacterial inocula and reactant solutions were added daily to sandy soil columns (6.5 cm height and inner diameter of 7.7 cm), while precipitation of CaCO₃ being investigated within 0-1.5, 1.5-3, 3-4.5 and 4.5-6 cm intervals. Chemical and micromorphological analyses revealed that CaCO₃ formation, inorganic C sequestration, and depth of cementation were more profound for S. pasteurii as compared with S. ureae. Both microbial CaCO₃ precipitation and inorganic C sequestration increased with increase in reaction time from 12 to 288 hours. Increase in reactant concentration also caused an increase in CaCO₃ precipitation (by 12%). Micromorphological observations showed a high degree of calcite crystals’ bridging, coating on sand particles and as well infilling of pore spaces. S. pasteurii is thus recommended for being used in stabilization of sand dunes; due to its significant effects on CaCO₃ deposition and as well on sand grain cementation.